Inorganic sheet material



INVENTOR.

v M HT 70PM? 1952 A. w. BROWN INORGANIC SHEET MATERIAL Flled July 9,1949 Patented Dec. 9, 1952 INORGANIC SHEET MATERIAL Alfred Winsor Brown,Ridgewood, N. J assignor to Owens-Corning Fiberglas Corporation, a

corporation ofDelaware Application July 9, 1949, Serial No. 103,840

4 Claims. 1

This invention relates tosheet material and particularly to an inorganicfabric'useful as electrical insulating tape but useful also in manyother applications.

In the construction of insulated electrical conductors and cables thereis need for a high temperature-resistant tape as a wrapping overtheconductor to insulate the conductor from objects'with which it is incontact, or to insulate the conductors in a multi-conductor cable fromeach other and from the sheath.

The most commonly used tape for this application is interwoven asbestosyarns, asbestos being used because it has high temperature resistance so.that when a short circuit occurs the asbestos will not fuse but remainin place as a .spacer to prevent contact of th conductor with otherconductors or with'adjacent objects such as the sheath.

.However asbestos tapes for this application have very exactingspecifications and are difiicult to manufacture because the tapes mustbe relatively thin, say .005 to .010 of an inch in thickness, andconsequently the yarns must be fine and fine yarns are diflicult toproduce from any but high quality asbestos fibers. The tapes must alsohav considerable tensile strength to permit their being tightly wrappedon the conductorand this strength requirement often dictatesthe'inclusion of reinforcing cotton strands. The reinforcement, ofcourse, detracts from the quality of the tape since a tape so reinforcedis not completely inorganic and this tape is unsuited for a number ofapplications.

It is an object of th present invention to provide a tape of other formof sheet material that is substantially completely inorganic andcontains sufficient asbestos to have exceedingly high temperatureresistance and in other respects partake of the nature of an asbestostape, but that does not require fine asbestos yarns and that may in factbe made of the much lower grade, shorter asbestos fibers.

It is another object of the invention to provide inorganic sheetmaterial that has high ternperature resistance coupled with exceptionaltensile strength, much higher strength than can be obtained even withquality asbestos yarns, with the result that the strength of the productmay be enhanced while the cost of the product is reduced.

The foregoing as well as other objects will be made more apparent asthis description proceeds.

In the accompanying drawing:

Figure l is a perspective-view on an enlarged scale of the inventionshown in the form of tape; and

Figure 2 is a diagrammatic view illustrating the process for making theproduct of the present invention.

The invention provides inorganic sheet material such as a tape in whichwebs of interfelted asbestos fibers are reinforced with fine yarnsdisposed in the direction of the tensile stresses to which the tape willbe subjected in use. The yarns are preferably in th form of an openweave fabric and the asbestos'webs are preferably disposed on oppositesides of the fabric and in contact with each other through the meshes ofthe fabric so that the webs ar tightly held together and the compositeproduct has a high degree of mass integrity.

Referring to Figure 1, the invention is shown inthe form of a tape l2made up of two webs l3 and M of interfelted asbestos having interjacentthe webs an open weave fabric 15 of interwoven glass fiber yarns. Thistape may be quite thin, its overall thickness being as low as .007 to0.10 inch. A thin tape of this character may be formed with an openweave fabric of approximately .003 to .005 inch thickness covered onopposite sides with asbestos webs of .002 or .003 inch thickness.

The asbestos webs are in contact with each other through the intersticesin the open weave fabric as shown at 15 and the webs are adheredtogether at these points as by being brought into contact while wet orby having an adhesive sprayed onto the adjoining faces before thewebsare laminated.

The use of an interwoven fabric of the kind described has considerableadvantage over the use of parallel strands or fibers to reinforce thecomposite product because not only is the fabric reinforced producteasier to fabricate but there is also reduced tendency to splitting ofthe tape lengthwise during application of the tape to a conductor.

The reinforcing fabric is most desirably a leno weave but otherconventional weaves are useful.

Figure 2 illustrates the method in which the product of the presentinvention may be made although, of course, it may be made in any othersuitable fashion if desired. The asbestos web l3 and 14 are representedas being formed on conventional paper making equipment. The station atwhich each web is formed includes a conventional beater 2| in which theasbestos is highly dispersed in water. From the beater the asbestosslurry spills onto a continuous paper making belt 22 and the web is thenpressed by being passed through rolls 23 for expressing excess water andto press the web to desired density. The webs from the two stations arebrought together into superposed relation and passed between a pair ofrolls 24 which exert sufi'icient pressure to cause the wet asbestos websto adhere together. To increase adherence, a small amount, say 1 or 2per cent by weight of the dry asbestos, of adhesive such as gum, rosin,starch, gelatin or the like, may be incorporated in the asbestos slurryin the beater. Alternatively the faces of the webs to be brought intocontact may have a coating of adhesive applied to them by means of sprayguns 25 stationed in advance of the duplexing rolls 24.

At the time the webs l3 and It are brought together the open weave glasscloth l5, supplied from a roll thereof or from other source, is fed intothe bite between the rolls so as to be en; closed between the asbestoswebs.

The glass fabric is preferably woven of relatively fine yarns, say yarnsof the 450 size, that is, yarns in which there are 45,000 yards to thepounds, and the yarns are preferably of two-ply but may be singles ifdesired. The woven fabric contains approximately 12 ends per inch inboth the warp and fill but it may be more open or more closely woven ifdesired. 10 ends or even less per inch are sufiicient where averagetensile strengths are desired but higher tensile strengths dictate theuse of as many as 20 or more ends per inch. These fine yarns and thiswide spacing of the yarns contributes greatly to a product in which thewebs are securely joined to each other.

As the asbestos webs and the glass cloth pass between the rolls 24, thepressure exerted by the rolls squeezes the asbestos webs into contactwith each other through the openings in the cloth with the result thatthe wet asbestos webs adhere to each other and when dried form acomposite fabric having an exceptionally high degree of integrity. Afterpassing the rolls, the composite fabric is dried in suitable fashion andmay be further treated in any conventional manner. It may be impregnatedor coated with electrical insulating varnishes or resins, it may belaminated with mica, or with other fabrics of the same or differentcharacter, and it may be dyed, printed, or otherwise colored.

While webs made wholly of asbestos are desired, the webs may containsmall amounts of other fibers. For instance, cotton may be added to theasbestos slurry during the beating operation, especially where shortasbestos fibers are used, for the purpose of increasing the interfeltingaction when the slurry is formed into a web. It has also been foundbeneficial to add 5 or per cent short glass fibers of about .0002 to.0003 inch in diameter and about A; to 4 inch long to the asbestosslurry to increase the interfelting action and resultantly the strengthof the asbestos web. The conventional adhesives and fillers may, of

course, also be added to the asbestos slurry as 6 desired.

The fabric of the present invention is particularly suitable forelectrical insulation but may be used wherever a substantiallycompletely inorganic sheet material of exceedingly high temperatureresistance is required as in the reinforcing of high temperature resinsor plastics. It is also well adapted to be coated or impregnated withresins and varnishes because the increased tensile strength imparted bythe reinforcing yarns permits easy handling of the sheet material whenwet with resins or varnishes and permits draping or festooning of thewet fabric in drying or curing ovens.

Various modifications may be made within the spirit of the invention andthe scope of the appended claims.

I claim:

1. An inorganic sheet material of extreme thinness in the order of .010inch or less and comprising a plurality of superposed webs ofinterfelted fibers of which part are glass and part are asbestos, and areinforcing fabric of glass yarns disposed between said webs, the fabricbeing of sufiiciently open weave to permit the Webs of interfeltedfibers to engage each other through the interstices in the fabric.

2. An inorganic sheet material of high tensile strength and extremethinness in the order of .010 inch and comprising a plurality of webs ofinterfelted asbestos fibers admixed with glass fibers, and a reinforcinginterwoven glass fabric disposed between said webs, the fabric being ofsufiiciently open weave to permit the webs of interfelted fibers toengage each other through the interstices in the fabric.

3. An inorganic sheet material of high tensile strength and extremethinness in the order of .010 inch and comprising a plurality of webs ofinterfelted fibers that are predominantly asbestos fibers, andreinforcing glass yarns disposed between said webs, the yarn being inparallel relation and being spaced apart sufliciently to permit the websof interfelted fibers to engage each other through the spaces betweenthe yarns.

4. An inorganic sheet material of high tensile strength and of athickness of no more than about .010 inch comprising a plurality of websof interfelted asbestos fibers, a reinforcing fabric interjacent two ofsaid webs and woven of fine glass yarns of the size in which there areap-' proximately 45,000 yards to a pound and the fabric having about 10to 20 ends per inch, whereby the fabric is of open weave, and portionsof the webs of interfelted fibers at opposite sides of the fabric beingin engagement with each other and adhered together through the openingsin said fabric.

ALFRED WINSOR BROWN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

